With the semiconductor devices formed with a semiconductor substrate in use, such defects of the semiconductor substrate as morphological defects such as concave and convex defects and crystal defects such as dislocations and stacking faults largely affect the performance, yielding and reliability of such devices. Such morphological defects and crystal defects are found especially on the silicon carbide substrate adopted for the semiconductor device for controlling power, so that it is extremely important that such substrate defects are inspected before such semiconductor device is manufactured. Thus, such inspection is performed in a non-destructive manner or on the premise that it does not affect the manufacturing steps of such semiconductor devices.
It is often that a silicon carbide substrate and a gallium nitride substrate are adopted for the materials of the above-mentioned semiconductor substrate. For the silicon carbide substrate, the silicon carbide substrate as it is or the substrate in which the epitaxial film made from the silicon carbide is formed on the silicon carbide substrate is often adopted. Further, for the gallium nitride, the substrate in which epitaxial growth of gallium nitride is performed on the silicone substrate is often adopted. Then, for such silicon carbide substrate and gallium substrate as well, it is important that their morphologic defects and crystal defects are inspected. Hereafter, the background art of the defects inspection of the silicon carbide substrate is described. To note, such background art also applies to the gallium substrate unless noted otherwise.
Then, as for the methods for inspecting such morphologic defects, such optical inspection methods are known as a differential interference contrast microscope method and a laser beam scattering method. Such inspection methods are also feasible to inspect even crystal defects just if there are morphologic features on the surface of a sample to be inspected (refer to Patent Literature 1 listed below). Further, as for the methods of inspecting such crystal defects, such methods are known as an X-ray topographic method, a transmission electron microscope method and an etch-pit method. However, the transmission electron microscope method and the etch-pit method lead to destroying a substrate, so that they are infeasible to apply for the non-destructive inspection adopted for a semiconductor substrate. Moreover, in the case of the methods where such defects are optically detected, the image resolution is susceptible to the restriction caused by the limit of wavelength of light.